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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_tr1.implementation"></a><a class="link" href="implementation.html" title="Implementation">Implementation</a>
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<p>
      When Boost.TR1 is <a class="link" href="config.html" title="Configuration">configured</a> to make
      use of your standard library's native TR1 implementation, then it doesn't do
      very much: it just includes the appropriate header.
    </p>
<p>
      When Boost.TR1 is using the Boost implementation of a particular component,
      then it includes the appropriate Boost header(s) and imports the necessary
      declarations in <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span></code> with
      using declarations. Note that only those declarations that are part of the
      standard are imported: the implementation is deliberately quite strict about
      not including any Boost-specific extensions in <code class="computeroutput"><span class="keyword">namespace</span>
      <span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span></code>, in order to catch any portability errors
      in user code. If you really need to use Boost-specific extensions then you
      should include the Boost headers directly and use the declarations in <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span></code> instead. Note that this style of implementation
      is not completely standards-conforming, in particular it is not possible to
      add user-defined template specializations of TR1 components into <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span></code>. There
      are also one or two Boost libraries that are not yet fully standards conforming,
      any such non-conformities are documented in <a class="link" href="subject_list.html" title="TR1 By Subject">the
      TR1 by subject section</a>. Hopefully, occurrences of non-standard behavior
      should be extremely rare in practice however.
    </p>
<p>
      If you use the standard conforming header includes (in <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">tr1</span><span class="special">/</span><span class="identifier">tr1</span></code>) then these header names can sometimes
      conflict with existing standard library headers (for example <code class="computeroutput"><span class="identifier">shared_ptr</span></code> is added to the existing standard
      library header <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">memory</span><span class="special">&gt;</span></code> rather than it's own header). These headers
      forward on to your existing standard library header in one of two ways: for
      gcc it uses <code class="computeroutput"><span class="preprocessor">#include_next</span></code>,
      and for other compilers it uses the macro <code class="computeroutput"><span class="identifier">BOOST_TR1_STD_HEADER</span><span class="special">(</span><span class="identifier">header</span><span class="special">)</span></code>
      (defined in <a href="../../../boost/tr1/detail/config.hpp" target="_top">boost/tr1/detail/config.hpp</a>)
      which evaluates to <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special">&lt;../</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">header</span><span class="special">&gt;</span></code>.
      This should work "straight out the box" for most compilers, but does
      mean that these headers should <span class="bold"><strong>never</strong></span> be placed
      inside a directory called "include" that is already in your compiler's
      search path.
    </p>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2005 John Maddock<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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